build, docs: Improve macOS building

- New docker command for quickly running tasks in a Linux environment.
- Updated docs with macOS specific details.
- Fixed some test issues.
- Add (fallible) macOS test target for Travis.

misc/make-deps.sh

@@ -39,7 +39,8 @@ if [ ! -z "$APT" ]; then
 fi
 
 if [ ! -z "$BREW" ]; then
-	$BREW install libvirt || true
+	# coreutils contains gtimeout
+	$BREW install libvirt augeas coreutils || true
 fi
 
 if [ ! -z "$PACMAN" ]; then